/*
    *
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.hadoop.hbase.filter;
  
  import java.util.ArrayList;
  
  import org.apache.hadoop.hbase.util.ByteStringer;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.KeyValueUtil;
  import org.apache.hadoop.hbase.exceptions.DeserializationException;
  import org.apache.hadoop.hbase.protobuf.generated.FilterProtos;
  import org.apache.hadoop.hbase.util.Bytes;
  
  import com.google.common.base.Preconditions;
  import com.google.protobuf.InvalidProtocolBufferException;
  
  /**
   * A filter, based on the ColumnCountGetFilter, takes two arguments: limit and offset.
   * This filter can be used for row-based indexing, where references to other tables are stored across many columns,
   * in order to efficient lookups and paginated results for end users. Only most recent versions are considered
   * for pagination.
   */
  @InterfaceAudience.Public
  @InterfaceStability.Stable
  public class ColumnPaginationFilter extends FilterBase
  {
    private int limit = 0;
    private int offset = -1;
    private byte[] columnOffset = null;
    private int count = 0;
  
    /**
     * Initializes filter with an integer offset and limit. The offset is arrived at
     * scanning sequentially and skipping entries. @limit number of columns are
     * then retrieved. If multiple column families are involved, the columns may be spread
     * across them.
     *
     * @param limit Max number of columns to return.
     * @param offset The integer offset where to start pagination.
     */
    public ColumnPaginationFilter(final int limit, final int offset)
    {
      Preconditions.checkArgument(limit >= 0, "limit must be positive %s", limit);
      Preconditions.checkArgument(offset >= 0, "offset must be positive %s", offset);
      this.limit = limit;
      this.offset = offset;
    }
  
    /**
     * Initializes filter with a string/bookmark based offset and limit. The offset is arrived
     * at, by seeking to it using scanner hints. If multiple column families are involved,
     * pagination starts at the first column family which contains @columnOffset. Columns are
     * then retrieved sequentially upto @limit number of columns which maybe spread across
     * multiple column families, depending on how the scan is setup.
     *
     * @param limit Max number of columns to return.
     * @param columnOffset The string/bookmark offset on where to start pagination.
     */
    public ColumnPaginationFilter(final int limit, final byte[] columnOffset) {
      Preconditions.checkArgument(limit >= 0, "limit must be positive %s", limit);
      Preconditions.checkArgument(columnOffset != null,
                                  "columnOffset must be non-null %s",
                                  columnOffset);
      this.limit = limit;
      this.columnOffset = columnOffset;
    }
  
    /**
     * @return limit
     */
    public int getLimit() {
      return limit;
    }
  
    /**
     * @return offset
     */
    public int getOffset() {
      return offset;
    }
  
   /**
    * @return columnOffset
    */
   public byte[] getColumnOffset() {
     return columnOffset;
   }
 
   @Override
   public ReturnCode filterKeyValue(Cell v)
   {
     if (columnOffset != null) {
       if (count >= limit) {
         return ReturnCode.NEXT_ROW;
       }
       byte[] buffer = v.getQualifierArray();
       if (buffer == null) {
         return ReturnCode.SEEK_NEXT_USING_HINT;
       }
       int cmp = 0;
       // Only compare if no KV's have been seen so far.
       if (count == 0) {
         cmp = Bytes.compareTo(buffer,
                               v.getQualifierOffset(),
                               v.getQualifierLength(),
                               this.columnOffset,
                               0,
                               this.columnOffset.length);
       }
       if (cmp < 0) {
         return ReturnCode.SEEK_NEXT_USING_HINT;
       } else {
         count++;
         return ReturnCode.INCLUDE_AND_NEXT_COL;
       }
     } else {
       if (count >= offset + limit) {
         return ReturnCode.NEXT_ROW;
       }
 
       ReturnCode code = count < offset ? ReturnCode.NEXT_COL :
                                          ReturnCode.INCLUDE_AND_NEXT_COL;
       count++;
       return code;
     }
   }
 
   // Override here explicitly as the method in super class FilterBase might do a KeyValue recreate.
   // See HBASE-12068
   @Override
   public Cell transformCell(Cell v) {
     return v;
   }
 
   @Override
   public Cell getNextCellHint(Cell kv) {
     return KeyValueUtil.createFirstOnRow(
         kv.getRowArray(), kv.getRowOffset(), kv.getRowLength(), kv.getFamilyArray(),
         kv.getFamilyOffset(), kv.getFamilyLength(), columnOffset, 0, columnOffset.length);
   }
 
   @Override
   public void reset()
   {
     this.count = 0;
   }
 
   public static Filter createFilterFromArguments(ArrayList<byte []> filterArguments) {
     Preconditions.checkArgument(filterArguments.size() == 2,
                                 "Expected 2 but got: %s", filterArguments.size());
     int limit = ParseFilter.convertByteArrayToInt(filterArguments.get(0));
     int offset = ParseFilter.convertByteArrayToInt(filterArguments.get(1));
     return new ColumnPaginationFilter(limit, offset);
   }
 
   /**
    * @return The filter serialized using pb
    */
   public byte [] toByteArray() {
     FilterProtos.ColumnPaginationFilter.Builder builder =
       FilterProtos.ColumnPaginationFilter.newBuilder();
     builder.setLimit(this.limit);
     if (this.offset >= 0) {
       builder.setOffset(this.offset);
     }
     if (this.columnOffset != null) {
       builder.setColumnOffset(ByteStringer.wrap(this.columnOffset));
     }
     return builder.build().toByteArray();
   }
 
   /**
    * @param pbBytes A pb serialized {@link ColumnPaginationFilter} instance
    * @return An instance of {@link ColumnPaginationFilter} made from <code>bytes</code>
    * @throws DeserializationException
    * @see #toByteArray
    */
   public static ColumnPaginationFilter parseFrom(final byte [] pbBytes)
   throws DeserializationException {
     FilterProtos.ColumnPaginationFilter proto;
     try {
       proto = FilterProtos.ColumnPaginationFilter.parseFrom(pbBytes);
     } catch (InvalidProtocolBufferException e) {
       throw new DeserializationException(e);
     }
     if (proto.hasColumnOffset()) {
       return new ColumnPaginationFilter(proto.getLimit(),
                                         proto.getColumnOffset().toByteArray());
     }
     return new ColumnPaginationFilter(proto.getLimit(),proto.getOffset());
   }
 
   /**
    * @param other
    * @return true if and only if the fields of the filter that are serialized
    * are equal to the corresponding fields in other.  Used for testing.
    */
   boolean areSerializedFieldsEqual(Filter o) {
     if (o == this) return true;
     if (!(o instanceof ColumnPaginationFilter)) return false;
 
     ColumnPaginationFilter other = (ColumnPaginationFilter)o;
     if (this.columnOffset != null) {
       return this.getLimit() == this.getLimit() &&
           Bytes.equals(this.getColumnOffset(), other.getColumnOffset());
     }
     return this.getLimit() == other.getLimit() && this.getOffset() == other.getOffset();
   }
 
   @Override
   public String toString() {
     if (this.columnOffset != null) {
       return (this.getClass().getSimpleName() + "(" + this.limit + ", " +
           Bytes.toStringBinary(this.columnOffset) + ")");
     }
     return String.format("%s (%d, %d)", this.getClass().getSimpleName(),
         this.limit, this.offset);
   }
 }